To provide a simple device for improving luminance of back light providing high luminance in the direction of the front inexpensively.

A manufacturing method for a lens sheet used for the back light includes a mold releasing agent forming process for providing mold releasing agent in only a tip part of a lens part provided on one face side of the lens sheet, a lens part surface reflection layer forming process for forming a reflection layer over the whole area of a side face of the lens part behind a section of the mold releasing agent provided in the mold releasing agent forming process, and a reflection layer removing process for removing the reflection layer formed on a surface of the mold releasing agent in the reflection layer formed in the lens part surface reflection layer forming process.